Pressure-sensitive adhesives are well known, and are used in a wide variety of label and tape applications. Such adhesives may be applied to, for example, paper, plastic films, metal, etc. to form the aforementioned labels or tapes. These labels and tapes may be affixed to a wide variety of substrates, and in many cases are removable or repositionable.
Pressure-sensitive hot melt adhesive systems are known in the art and consist of tackified thermoplastic elastomers such as styrenic block copolymers together with tackifying resin(s) and generally some plasticizing oil, an antioxidant and optionally fillers. Styrenic block copolymers containing polystyrene and polybutadiene blocks and/or polyisoprene blocks are particularly useful. These materials are generally available as pure triblocks, (sometimes referred to as SIS and SBS copolymers), and diblocks (sometimes referred to as SI and SB copolymers or SIB copolymers). The materials are also available as mixtures of diblock and triblock materials (sometimes referred to as SIS+SI and SIS+SB).
It is known to use diblock/triblock blends as the elastomeric component in hot-melt pressure-sensitive adhesives. It is further known that adhesive properties and viscosity can be controlled by varying the diblock-to-triblock ratio, varying the styrene content, varying the polymer molecular weight, and varying the block molecular weights within the polymers. The melt viscosity can also be controlled by the addition of plasticizing oils and varying the molecular weight of the polymers.
One drawback of such adhesive formulations is that, in order to achieve the desired processability and removability of a product, many additives such as silicone oils, waxes, and other fillers must be added. Incorporation of such additives leads to increased expense, and also limits the equipment that may be used to manufacture the adhesive compositions.
U.S. Pat. No. 5,523,343 discloses a pressure sensitive hot melt adhesive composition comprising a blend of a radial SB copolymer and a SIS block copolymer. The composition also includes a tackifier resin and plasticizer oils.
U.S. Pat. No. 6,384,138 discloses a hot melt pressure sensitive adhesive composition for use with oriented polypropylene films which comprises a blend of styrene-isoprene-styrene (SIS) and styrene-butadiene-styrene (SBS) block copolymers combined with a blend of hydrocarbon resins.
U.S. Application Pub. No. 2009/0133834 discloses radial block copolymer compositions and pressure-sensitive adhesive compositions based thereon.
It would be useful, therefore, to develop an adhesive composition for use with labels and/or tapes having the properties of a typical block copolymer-based adhesive at a lower cost and with increased processability. The invention described herein accomplishes this by blending a block copolymer component with a hydrocarbon tackifier resin component and a propylene-based polymer component.